The present disclosure relates to an image processor and an image processing method, and more particularly to an image processor and an image processing method that inhibit production of a phase shift in a color difference signal in intra prediction.
In recent years, apparatuses in conformity with a scheme, such as MPEG (moving picture experts group), that handles image information digitally, and at that occasion, compresses by orthogonal transformation, such as discrete cosine transform, and motion compensation for highly efficient transmission and accumulation of information utilizing the redundancy typical of the image information have been widespread in both information distribution of a broadcasting station and the like and information reception in households.
In particular, MPEG2 (ISO (International Organization for Standardization)/IEC (International Electrotechnical Commission) 13818-2) is defined as general purpose image encoding, is a standard that covers both interlaced scanning images and progressive scanning images and also standard resolution images and high resolution images, and is currently widely used for a wide range of applications for professional use and consumer use. By using MPEG2 compression, for example, an amount of coding (bit rate) of from 4 to 8 Mbps is allocated to an interlaced scanning image of standard resolution having 720×480 pixels and an amount of coding (bit rate) of from 18 to 22 Mbps is allocated so an interlaced scanning image of high resolution having 1920×1088 pixels, thereby enabling a high compression rate and good image quality.
MPEG2 is mainly directed to high image quality encoding adapted to broadcasting, while it toes not correspond to encoding of an amount of coding (bit rate) lower than MPEG1, that is, of a higher compression rate. For the widespread mobile phone terminals, above-mentioned encoding may be increased in the future, and corresponding to this, MPEG4 encoding may be standardized. Regarding image encoding, the specification of ISO/TEC 14496-2 is approved as an international standard in December 1998.
Further, in recent years, initially for the purpose of image encoding for video conference, a standard of H.26L (ITU-T (International Telecommunication Union Telecommunication Standardization Sector) Q6/16 VCEG (Video Coding Expert Group)) is advancing in normalization. It is understood that H.26L enables higher encoding efficiency while requesting a more amount of arithmetic operations for encoding and decoding thereof compared with encoding in the past, such as MPEG2 and MPEG4. In addition, currently, as part of the MPEG4 activity, standardization is carried out as Joint Model of Enhanced-Compression Video Coding that enables higher encoding efficiency by incorporating functions not supported by H.26L as well on the basis of the H.26L.
As a schedule for standardization, the H.26L standard became an international standard in the name of H.264 and MPEG-4 Part10 (advanced video coding, hereinafter referred to as AVC) in March 2003.
In AVC, a hierarchical structure with macroblocks and submacroblocks as processing units for encoding (encoding units) is defined. However, is not optimal to have the macroblock size of 16 pixels×16 pixels for a large image frame, such as a UHD (ultra high definition; 4000 pixels×2000 pixels), as subjected to next generation encoding.
With that, in HEVC (high efficiency video coding) to be post AVC encoding, a coding unit (CU) is defined as an encoding unit instead of the macroblock (for example, refer to Benjamin Bross, Woo-Jin Han, Jens-Rainer Ohm, Gary J. Sullivan, Thomas Wiegand, “Working Draft 4 of High-Efficiency Video Coding”, JCTVC-F803_d2, Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11 6th Meeting: Torino, IT, 14-22 Jul., 2011).
In such AVC and HEVC, many modes are prepared for intra prediction. As one of them, for example, there is proposed intra prediction of a color difference signal (LM (linear model) mode) utilizing correlationship between a luminance signal and a color difference signal (for example, refer to Jianle Chen, Vadim Seregin, Woo-Jin Han, Jungsun Kim, Eyeongmoon Jean, “CE6.a.4: Chroma intra prediction by reconstructed luma samples”, JCTVC-E266, Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11 5th Meeting: Geneva, 16-23 Mar., 2011).